Nagios needs to be restarted after adding/removing config files

The "writeconf" method (backend/nagios/systemapi.py) of the Nagios module restarts the Nagios service after writing configuration files.

For the Ceph module we have two special methods "write_nagios_configs" and "remove_nagios_configs" (backend/ceph/systemapi.py). These methods doesn't restart the Nagios service yet. So after creating the Ceph configuration files, no .rrd files will be created for the clusters.

Possible solution:
Wrap the restart of the Nagios service in backend/nagios/systemapi.py by its own DBus method and call this method from the Ceph module.